Brown W C, Estes D M, Chantler S E, Kegerreis K A, Suarez C E
Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, Washington 99164, USA.
Infect Immun. 1998 Nov;66(11):5423-32. doi: 10.1128/IAI.66.11.5423-5432.1998.
DNAs from bacteria and variety of nonvertebrate organisms, including nematodes, mollusks, yeasts, and insects, cause polyclonal activation of murine B lymphocytes. Similar studies have not been reported for bovine B cells, and to date no studies have reported mitogenic properties of protozoal DNA for any species. However, we and others have observed that protozoal parasite antigens can induce the proliferation of lymphocytes from nonexposed donors. Extending these studies, we now show that the mitogenic property of protozoal antigen preparations is in part attributable to parasite DNA and that Babesia bovis DNA is directly mitogenic for bovine B cells. DNase treatment of B. bovis extracts abrogated B. bovis-induced proliferation of peripheral blood mononuclear cells from nonexposed cattle. Like DNAs from other organisms that were mitogenic for murine B cells, B. bovis DNA is largely nonmethylated and induced a dose-dependent proliferation of bovine B cells, which was reduced upon methylation. Furthermore, B. bovis and E. coli DNAs enhanced immunoglobulin secretion by cultured B cells, inducing moderate increases in immunoglobulin G1 and stronger increases in immunoglobulin G2. Because certain nonmethylated CpG motifs present in bacterial DNA are known to stimulate proliferation of murine and human B cells, an 11-kb fragment of B. bovis DNA was analyzed for CG dinucleotide content and for the presence of known immunostimulatory sequences (ISS) centered on a CG motif. The frequency of CG dinucleotides was approximately one-half of the expected frequency, and several CpG hexameric sequences with known activity for murine B cells were identified. An oligodeoxynucleotide containing one of these ISS (AACGTT), which is present within the rhoptry-associated protein-1 (rap-1) open reading frame, was shown to stimulate B-cell proliferation. These ISS may be involved in host immune modulation during protozoal infection and may be useful as vaccine adjuvants.
来自细菌以及包括线虫、软体动物、酵母和昆虫在内的多种非脊椎动物的DNA，可引起小鼠B淋巴细胞的多克隆激活。关于牛B细胞，尚未有类似的研究报道，并且迄今为止，尚无关于原生动物DNA对任何物种的促有丝分裂特性的研究报道。然而，我们和其他人观察到原生动物寄生虫抗原可以诱导未接触过的供体的淋巴细胞增殖。在这些研究的基础上，我们现在表明原生动物抗原制剂的促有丝分裂特性部分归因于寄生虫DNA，并且牛巴贝斯虫DNA对牛B细胞具有直接促有丝分裂作用。用脱氧核糖核酸酶处理牛巴贝斯虫提取物可消除牛巴贝斯虫诱导的未接触牛外周血单个核细胞的增殖。与对小鼠B细胞有促有丝分裂作用的其他生物体的DNA一样，牛巴贝斯虫DNA在很大程度上未甲基化，并诱导牛B细胞剂量依赖性增殖，甲基化后增殖减少。此外，牛巴贝斯虫和大肠杆菌的DNA增强了培养的B细胞的免疫球蛋白分泌，使免疫球蛋白G1适度增加，免疫球蛋白G2增加更明显。由于已知细菌DNA中存在的某些非甲基化CpG基序可刺激小鼠和人类B细胞增殖，因此对牛巴贝斯虫DNA的一个11kb片段进行了CG二核苷酸含量分析以及以CG基序为中心的已知免疫刺激序列（ISS）的存在分析。CG二核苷酸的频率约为预期频率的一半，并鉴定出几个对小鼠B细胞具有已知活性的CpG六聚体序列。含有这些ISS之一（AACGTT）的寡脱氧核苷酸，其存在于棒状体相关蛋白-1（rap-1）开放阅读框内，被证明可刺激B细胞增殖。这些ISS可能参与原生动物感染期间的宿主免疫调节，并且可能用作疫苗佐剂。
